1. Field of the Invention
The present invention relates to an optical apparatus and optical system for illuminating a predetermined target object by a light source.
2. Related Background Art
Conventionally, reading devices used in a facsimile apparatus, an electronic copying machine, and other information processing apparatuses, use as an illumination unit for illuminating an original to be read, a discharge tube such as a fluorescent tube, and an LED array prepared by arranging many LED (Light Emitting Diode) chips in an array. Particularly in recent years, most of reading devices use LED arrays in the facsimile apparatus and the like because small, low-cost products are required along with the use in home. To decrease the number of LED chips to be used and realize a lower-cost product, some reading devices employ a light source in which an LED chip is arranged at the end portion of a rod-shaped transparent member formed of a transparent glass, a resin, or the like, and a beam emitted from the LED chip is linearly expanded using internal reflection inside the transparent member to irradiate the beam onto the original surface to be read.
FIG. 7 is a sectional view showing such a reading device. In FIG. 7, an original A has an image to be read on its surface. A light source B illuminates the original. A rod lens array C images a beam reflected by the original surface on a sensor surface. A sensor (also called line sensor) D is arranged in this reading device. A housing E holds the light source B, the rod lens array C, and the sensor D. A glass plate F holds the original A.
The light source B is constituted by combining a rod-shaped light guide 3 having an area 5 for reflecting and/or scattering the beam on part of its surface and formed from a transparent material, and an LED chip (not shown) arranged at an end portion of the transparent member.
FIG. 8 is a schematic view for explaining the function of the light source indicated by B in FIG. 7. FIG. 8 is a perspective view additionally showing an LED chip 1 arranged at an end portion of the light guide 3.
A beam emitted from the LED chip 1 and incident into the light guide 3 is repeatedly reflected by the inner surface of the light guide 3 and propagates in the light guide 3. When the beam is incident on an area 5 during the repeated reflection, it is diffused. Since the diffused beam ceases to satisfy the total reflection conditions, it emerges from the light guide 3, and its part linearly illuminates the target reading area of the original.
If only an LED chip having a single emission color is used as the LED chip 1, the reading device reads monochromatic image information. If color image information is to be read, a plurality of LED chips having different emission colors such as red, blue, and green are arranged. The LED chips having the respective emission colors are sequentially switched at a high speed, and caused to emit beams. In synchronism with this, accumulation and read-out of signal changes are performed in the sensor D.
For example, when, of the LED chips arranged at the end portion of the transparent member B, the red-light-emitting chip emits a beam, the target reading portion of the original is illuminated with a red beam. At this time, the beam reflected by the original and imaged by the converging rod lens array C gives red information of the image on the original surface to a signal to be accumulated as an accumulated charge in the sensor D. When the blue- and green-light-emitting LED chips emit beams, signals have blue information and green information, respectively.
In this reading device, a beam exit surface 6 of the light source B is located near the rod lens array C, unlike in a reading device using an LED array. For this reason, part of the beam which emerges from the beam exit surface 6 of the light source B, or part of the beam reflected by the housing E is directly incident on an incident surface C-1 of the rod lens array C, and becomes an unwanted flare beam which degrades the quality of the read image.